In recent years, in particular, there has been a demand for realizing a flexible optical wiring to be mounted (similar to electrical wiring) on bendable displays and more compact and thin commercial-off-the-shelf equipments with an optical waveguide.
In applications such as portable terminal, in particular, there has been desired a new wiring capable of forming patterns such as the conventional FPC (printed circuit board), and having flexibility (particularly twistability) and noise-resistance property such as coaxial cable, and in that sense, there has been desired a new wiring which uses a bendable, twistable, and flexible film-type optical waveguide.
The optical waveguide is formed by a core having a large index of refraction, and a clad having a small index of refraction arranged contacting the periphery of the core, and is made to propagate an optical signal entered to the core while repeating total reflection at the boundary of the core and the clad.
There is a need to align with and optically couple with a photoelectric conversion element (fight receiving/emitting element) to transmit optical data using the optical waveguide. The light receiving/emitting element converts an electric signal to an optical signal and transmits the optical signal, and receives the optical signal and converts the optical signal to the electric signal. In order to maintain the optically coupled state, the distance and the position relationship of a receiving/transmitting part of the optical signal in the light receiving/emitting element and an entrance/exit port of the optical signal in the optical waveguide need to be maintained constant with the optical cable fixed.
Conventionally various methods have been proposed to fix the optical cable to optically couple the optical cable and the light receiving/emitting element.
For instance, when using an optical fiber for the optical cable, there is adopted a method of attaching a holding member (ferrule) at an end of the optical fiber and fixing the holding member to a package. The entrance/exit port of the optical signal in the optical fiber is thereby fixed, and the optically coupled state can be maintained.
When using an optical waveguide for the optical cable, there is adopted a method of forming an insertion hole in a package, and directly inserting the optical waveguide into the insertion hole to be fixed to the package. One example of this method is described in patent document 1. The conventionally used optical waveguide has rigidity compared to the film-type optical waveguide, and thus a holding member such as ferrule is unnecessary, and the structure thereof is not described.
FIG. 30 is a perspective view showing a schematic configuration of an optical module 100 described in patent document 1, and FIG. 31 is a perspective view showing a schematic configuration of a package of the optical module 100. As shown in FIG. 31, an insertion port 103 is formed in a package 101 to insert an optical waveguide 102. The optical waveguide 102 is inserted to the insertion part 103 and fixed so that a semiconductor laser (light receiving/emitting element) 104 arranged inside the package 101 and the optical waveguide 102 optically couple. The distance and the position relationship of the optical waveguide 102 and the light receiving/emitting element 104 are thereby maintained constant.
A method of fixing the optical waveguide when using an optical waveguide having high flexibility for the optical cable is disclosed in patent documents 2 and 3. Specifically, the optical waveguide is directly fixed to the light receiving/emitting element using an adhering member such as adhesive.
Patent document 1: Japanese Laid-Open Patent Publication No. 6-82660 (Published Mar. 25, 1994)
Patent document 2; Japanese Laid-Open Patent Publication No. 2003-302544 (Published Oct. 24, 2003)
Patent document 3: Japanese Laid-Open Patent Publication No. 2004-21042 (Published Jan. 22, 2004)
The conventional configurations described above have the following problems.
The method of fixing the optical waveguide with the holding member such as ferrule used as a connecting technique of a rigid optical waveguide is methodically difficult when using a very flexible optical waveguide due to its flexibility. Consideration is made in reinforcing the flexible optical waveguide with a rigid member, but a problem arises in the optical system, in which a 45 degrees mirror and the like are arranged, in that the outer shape of the distal end becomes large thereby shielding the optical path, and realization of a low height module becomes difficult particularly for the commercial-off-the-shelf equipments such as information terminal.
In the method described in patent document 1, the optical waveguide is fixed only by a side wall in a direction traversing the optical waveguide in the package, and an end of the optical waveguide projected to the inside of the package is not fixed, and thus the end of the optical waveguide deforms, and warp or the like occurs in a situation where the usage environment of the optical module changes by heat generation of peripheral components, external force of vibration/drop, and the like. As a result, the distance between the receiving/transmitting part of the optical signal in the light receiving/emitting element and the entrance/exit port of the optical signal in the optical-waveguide, as well as the position relationship in XYZ directions change, and the optical coupling efficiency fluctuates.
In particular, polymer waveguide is often used when using the film-type optical waveguide having high flexibility, in which case the coefficient of thermal expansion is large and the coefficient is constituted by the core and the clad having different flexibilities, and thus has a property of being susceptible to heat.
In the methods described in patent documents 2 and 3, a height direction becomes large and miniaturization becomes difficult since the light receiving/emitting element and the optical waveguide are directly joined with adhesive.
In view of the various problems described above, it is an object of the present invention to provide an optical module capable of achieving miniaturization and capable of suppressing fluctuation of optical coupling efficiency.